Field of the Invention
The present invention relates to an image forming apparatus.
Description of the Related Art
Conventionally, an intermediate transfer-type image forming apparatus is known, in which a toner image formed on a photosensitive drum is primarily transferred to an intermediate transfer belt, and the toner image formed on the intermediate transfer belt by primary transfer is secondarily transferred to the recording material. In this type of image forming apparatus, a transfer voltage is applied to a secondary transfer inner roller abutted against a secondary transfer outer roller with an intermediate transfer belt intervened and forming a secondary transfer portion, i.e., secondary transfer nip portion, by which secondary transfer is performed.
According to the above-described secondary transfer outer roller, an elastic layer is provided on a circumferential surface of a shaft portion having conductivity, and a conductive agent such as an ion conductive agent is dispersed in the elastic layer, giving conductivity to the elastic layer. In that case, however, along with the elapse of application time of transfer voltage, ions within the ion conductive agent polarize in a manner biased to a roller surface side or a shaft portion side, and electric resistance tends to be raised. When the electric resistance is raised, even if a same transfer voltage as before the resistance is raised is applied, it is difficult to supply the same amount of transfer current to the secondary transfer portion as before the resistance is raised. Therefore, in order to suppress the rising of electric resistance caused by polarization, for example, Japanese Unexamined Patent Application Publication No. 2005-316200 proposes an apparatus configured to supply current from a power feed roller abutted against a surface of a secondary transfer outer roller to a secondary transfer outer roller, which is referred to as external power feed, to transfer a toner image from an intermediate transfer belt to a recording material.
The image forming apparatus disclosed in the above-described Japanese Unexamined Patent Application Publication No. 2005-316200 adds the power feed roller to the secondary transfer unit in a state abutted against the secondary transfer outer roller, so that the secondary transfer unit may be increased in size compared to the conventional apparatus.